Response to "do vasomotor nerves significantly regulate cerebral blood flow?".

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Abstract
Purves presented the view that neural mechanisms may play a major role in regulation of cerebral resistance. This view is in contrast to that of the author, who deemphasized the importance of neural control except under unusual circumstances. Comments are made on several points that Purves made. Several questions must be answered before one can conclude that nerves have physiologically important effects on cerebral blood flow. Does reflex activation of neural pathways, as opposed to intense electrical stimulation, alter cerebral blood flow? Is the effect on flow trivial in magnitude, as in most experiments to this time, or are the effects of neural stimuli quantitatively important? Is the role of neural stimuli very circumscribed (e.g., only during severe hypertension), or do nerves play an important role during cerebral vascular responses to several physiological stimuli? When these questions are answered, significant progress will have been made toward resolving the controversy concerning the importance of neural mechanisms in control of cerebral blood flow. Nerves may have important cerebral vascular effects without altering blood flow significantly. It will be important to clarify the role of nerves in protection of the blood-brain barrier, in determining capillary surface area and in affecting cerebral blood volume.